Recovery of fluorspar from ores thereof



Patented Dec. 23, 1930 UNITED STAT-ES PATENT oFFicE;

JOHN CHARLES WILLIAMS, OF WESTPORT, OONNECTIGUT, AND WATSON GREE MAN, 01 MARION, KENTUCKY, ASSIGNORS TO ALUMINUM COMPANY, OF'AMEBICA, OF PITTSBURGH, PENNSYLVANIA, ACOBPOBATION OF PENNSYLVANIA I RECOVERY or rLuonsPAn. r301: onus THEREOF 1T0 Drawing.

This invention relates to a method of frothconcentrated from fluorspar ores and similar fluorspar bearing material, containing substantial amounts of calcite,

The minerals commonly found associated with fluorspar in mineableveins are quartz and calcite, and one or the other, depending upon the location of the fluorspar deposit, is usually the chief constituent of the gangue of the fluorspar ore. In the United States a predominant number of the mineable veins of fluorspar occur in limestone formation and inmost cases run in a direction vertical to the ground surface. ,In these veins the ore found near the surface chiefly contains silica as the gangue but as the vein strikes downwardly the quartz is replaced to a large extent by calcite and at a considerable depth the calcite content of the gangue becomes abnor-,'

mally high. Such ores may therefore contain, depending upon their location in the vein, from a relatively insignificant amount up to as much as 35 per cent or more of calcite. The term calcite as used in the present description and in the appended claims includes not only the substantially pure calcium carbonate found naturallyassociated with fluorspar but also other minerals in which calcium carbonate is the predominating constituent.

Fluorspar has a wide and varied application in the chemical, ceramic and metallurgical industries. as well as in others. The mmcral serves various purposes, ranging from a source of fluorine in chemical processes to a fluxing material in the manufacture ofsteel, and consequently it is furnished to meet a number of varying specifications as to analysis. The highest grade of fluorspar material on *the market is commercially known as acid grade s ar and is furnished to meet arequirement o 98 per cent or more of calcium fluoride. This content of calcium fluoride or even a somewhat lower content is not found in much of the ore as mined and therefore suitable methods of concentrating the lower grade ores to a product containing 90 per cent oigmore of calcium fluoride are of considerableiimportance.

Application filed September 26, 1928. Serial No. 308,576.

In developing such methods the industry has experimented for years with various types of well known concentrating treatments and there have been developed processes involving gravity separation, wet'or dry, and some methods of froth-flotation. By these processes ores containing large amounts of silicious gangue have been economically concentrated to products of higher purity but it has not been possible to obtain a satisfactory acid. grade concentrate from calcite-bearing ore, despite the fact that the large production 1 proportion of the slimes and other fine or-colloidal-sized material have first been removed from the finely divided ore.

- We have further observed, that the combinations of flotation reagents heretofore generally used forselective flotation of minerals do not produce a desirable efficiency of operation, even after pre-treatment of the ore in accordance with our invention. We have found, however, that by the use of a mixture of oleic acid and cresvlic acid or salts thereof, following our preliminary treatment of the ore, a degree'of calcite removal can be attained which to our knowledge has never been reached before by a commercially operable process. I

In the older attempts to obtain a selectiveflotation of fluorspar from calcite, or inversely, of calcite froin fluorspar, the'ore was first ground in a manner which had been demonstrated to lie-suitable in the treatment if of high silica fluorspar ore andother ores. The ground ore was subjected to a frothingoperation, usually without a preliminary removal of slimes; or, if a desliming operation was used, the removal of slimes was, as'our results have shown, incomplete.

In investigating these earlier processes and in developing the process of which our invention is a part, an extensive and careful series of tests was made. In all of these, several of which will be described herein, the following procedure was followed. The ore. after a preliminary grinding and with or without desliming depending upon the particular test, was'diluted with water to form a suitable pulp. The weight ratio of ore to water varied from 1 to 2 to 1 to 4 but generally a ratio of about 1 part of ore to 3 or 4 parts of water was found to give the best results. The pulp was placed in a laboratory type flotation cell and to it were added the flotation reagents. The mixture was aerated to form a froth which, rising and flowing over the lip. of the cell, carried with it the floatable or lifted material. This froth was suitably diluted with water and again floated with. or without the addition of further quantities of reagents. This last treatment, known as cleaning, was preferably repeated two or three times. ,The material lifted by the froth in the final cleaning operation was designated as the final concentrate.

Using such an operation as described above in conjunction with a preliminary grinding and desliming of the ore as heretofore practiced, a large number of tests were run on various fluorspar ores. The flotation reagents used in these experiments,-the hydrogen ion concentration of the pulp, the period of frothing, and similar factors, were varied in an effort to obtain a satisfactory separation of the fluorspar from the other constituents. The results of these tests confirmed previous conclusions, namely that the fluorspar could be satisfactorily separated from quartz or silicious impurities by various flotation methods but in no case was satisfactory flotation of fluorspar from calcite obtained.

For example, an ore with a silicious gangue, containing by analysis, 22 per cent SiO 1.7 per cent CaCO and 75 per cent CaF was ground dry, to pass a 100 mesh screen and thn ground wet for 30 minutes in a pebble mill with two parts of water. The resulting pulp was suitably diluted and submitted to a preliminary frothing with pine oil to remove the slimes. Of the original sample 4.7 per cent was removed in this desliming operation. The remaining pulp was frothed with oleic acid and soda ash and the resulting concentrate contained 0.45 per cent SiO 0.78 per cent qCECO and 98.75 per cent CaF Of the original calcium fluoride content of the ore, 78.3 per cent was recovered in the final concentrate.-

Such results are regarded as very satisfac tory and as equivalent to or better than the results obtained by" other methods of separation. Similar results are not, however, obtained with high calcite fluorspar ores, for when treated'by substantially the same procedure these ores yield a relatiyely low grade concentrate and the percentage recoveries of the original spar content are low. For instance, with an ore containing 16 per cent (laCO 2.5 per cent SiO and 80.5 per cent CaF the resulting final concentrate contained 11 per cent CaCO 0.02 per cent SiO andabout 88 per cent CaF Only 37.2 per cent of the calcium fluoride content of the original sample was recovered in the final concentrate. In these tests, as in similar ones, the calcium fluoride recovered was almost completely freed from the silica but only a small degree of separation of calcite and fluorspar was obtained.

Other tests carried out along the lines indicated were unsuccessful and gave no better results. Attempts to exert a depressing effect upon the calcite by the addition of sulphates such as aluminum sulphate and copper sulphate were unsuccessful, as were also various combinations of reagents such as sodium oleate and soda ash, oleic acid and soda ash, oleic acid and pine oil, and other variations of these combinations.

Throughout the above mentioned experiments, which failed to selectively float the fluorspar or to result in a suitable recovery of calcium fluoride from the ore, the lead and zinc values were removed by means of a preliminary operation consisting in mixing with the pulp a suitable froth producing reagent and frothing the pulp for short periods. This operation incidentally removed a portion of the slimes present. In attempting to improve the results of the final frothing operation the preliminary frothing was carried out with agents, for example oleic acid, pine oil, copper sulphate, sodium sulphide, soda ash, and hosphocresylic acid, separately and in com ination. Regardless of the reagent used in the preliminary frothing operation a final concentrate of consistently low calcite content could not be obtained.

In the course of studying theresults of these experiments it occured to us that the failure was due in large measure to abnormal sensitiveness to colloidal interference of the slimes rather than to the type of selective wetting and frothing reagents used, and that removal of a substantial proportion of the slimes before frothing would give a higher fluorspar recovery and less calcite in the final concentrates, no matter what frothing reagents are employed. This was found to be a fact, and is shown, for example, by the following series of tests with an ore analyzing 16 per cent (laCO 2.5 per cent SiO 80 per cent CaF This ore was first dryground to pass a 100-mesh screen and then ground with two parts of water in a pebble mill.

t: r can 0 can 0 'gest Frgthlipgreagent used ore regi igf gi g gi calcite 0. 1n es immg operation urged mg (mentions ginilialt slimes trate 1--. No desliming opera- Copper sulphate so- 26.7

tron. dium sulphide and phosphocresylic acid. 2 Pine oil 5.7 Sodium oleate and 13.0

- soda ash. 3---" Copper sulphate and 8. 6 Oleic acid and phos- 15. 3

phosphocresylic phocresylic acid. aci 4 Pine oil 9. 1 Oleip1 acid and soda 11.3

as 5- Copper sulphate and 17.4 Oleic acid and phos- 2. 7 phosphocresylic phoeresylic acid. acid and sodium sulphide.

It Will be seen from these tabulated results that, although the flotation agents which were used in boththe preliminary and the final frothing operations vary from test to test, the amount of calcite in the final concentrate is a function of the amount of removed slimes rather than a functionof the different reagents. The treatment in tests 3 and 5 were practically identical but where the slimes removed in test 3 amounted to 8.6 per cent the final concentrate contained 15.3 per cent of CaCO; as compared with 2.7 per cent CaCO contained -in.the concentrate of test 5 after removal of 17.4 per cent of the ore as slimes. v

We have also found that to obtain the best results the preliminary grinding or other comminuting operation should be carefully done, in order to decrease as far as practically possible the amount of slime or material approaching colloidal dimensions. It will be understood that by the word slimes we mean the fine, or in some cases colloidal-sized, material occurring in the original ore and, as a result of grinding, in the ground ore. Preparatory to the desliming step of our process we have found it preferable to grind the ore to pass a screen of about 28 mesh and then to stage-grind this material with water in a pebble or ball 'mill until the greater portion of the ore will pass a mesh screen. However, the point to'be considered is the suppression of slime formation, and in the case of a given ore, any suitable grinding process by which a floatable product is obtained withoutthe production of a large amount of colloidal material should give the desired results. The desliming may be accomplished by frothing the pulp with suitable frothing reagents as before noted but weh'ave found it preferable to use a method of desliming wherein the ore is diluted Withwater, agitated, and allowed to settle for successive periods of about 5 minutes. Atthe end of each period the water and suspended matter are siphoned off or otherwise removed and water again added. The number of settling present in the ore do not float. as

treatments mus t be determined experiment but We have'found that generally good results may be produced by three settlings. It will be readily seen that-the desliming operation may be carried out by any means, it being only necessary to use such a "procedure as will. remove substantially all or at least a greater part of the fine or colloidal-sized particles.

Although desliming enables us to reduce the calcite content of the ore and obtain a finalconcentrate of excellent analysis and one which fully meets the required specifications, we have found that with some flotation reagents it isnot possible to consistently ob- .tain final concentrates which contain the spar and the calcite, and also produces a stiff and stable froth by which it is possible-to float both of these materials. However, the tendencies of fluorspar and calcite to float in such a froth are nearly equal, and the result would be a non-selective flotation yielding a high calcite concentrate and therefore an undesirable product, In order to depress the flotation tendency of the calcite Without decreasing the fluorspar tendency to the same extent we'pr'ovide a froth which will hold in its interfaces the particles of fluorspar but will be so tender that the calcite will not be raised at the same time. A highly selective froth of this type can be produced by modifying the oleic acid froth 'with additions of cresylic acid or phosphocresylic acid or other suitable reagent. By such additions the wet ting or oiling properties of the oleic acid, sodium oleate or other frothin-g agent, are apparently not impaired but the froth is made tender and as a result does not lift the calcite. With these reagents, recoveries as high as 85 to .98 per cent of the fluorspar value of the deslimed ore can be obtained in thefinal concentrate. The silica impurities which may be readily as eitherthe calcite or the fluorspar and hence their removal is effected along with the calcite.

In the preferred practice of our process we use oleic acid and cresylic acid, preferably in substantially equal quantities, as these 3 and cresylic acid or oleic acid and phosphocresylic acid may be used with satisfactory results and it is to be understood that in the claims appended hereto theterms oleic acid andcresylic acid include sodium oleate and phosphocresylic acid as their rcspectiy e equivalents.

Our invention, which comprises suitable removal of the slimes and subsequent flota-. tion of the deslimed ore, provides an efficient and easily operable method of concentrating fluorspar values from fluorspar ore. It is possible by means of this process to satisfactorily and economically recover fluorspar values from high calcite fluorspar ore or mixtures of calcite and fluorspar which heretofore have not been considered as practical sources of acid grade fluorspar. In general it is not necessary that the exact conditions of treatment herein described be observed, and

with a particular ore it may be necessary to vary to some extent the desliming operation and the proportion of the flotation agents used. As is well understood in the flotation art, the water used may exert a marked influence on theresults, and usually it is necessary to determine by trial the most advantageous kind of water. In the present case the most satisfactory results have been obtained with water having a pH value varying from 6.5 to 8, and a naturally soft water having a pH value around 7 will usually be found suitable, but the suitability of any particular water can easily be determined.

The following examples of the manner in whichour invention is preferably utilized are given.

Example 1 The original ore contained 21.5 per cent CaCO 6 per cent SiO and 70.8 per cent CaF This ore, after reduction to about onefourth inch size, was ground in a pebble mill to pass a mesh screen. The ground ore was then mixed with suitable amounts of water and deslimed by repeated settling for fiveminute periods, the water and suspended material being siphoned off to within. an inch of the ore after each five-minute period. The deslimed pulp was placed in a laboratory flotation machine and 0.3 pounds of oleic acid and 0.3 pounds of cresylic acid per ton of pulp were added. The mixture was frothed' for a suitable period and the froth, together with the material carried by it, was collected as it came over the lip of the cell. This froth was placed in another cell, diluted with water and without the addition of further reagents the pulp was againfrothed. This operation was twice repeated and the froth from the final operation taken as the final concentrate.

In this run 24.5 er cent of the ore was re moved as slimes. hese carried 21.1 per cent of the original calcium fluoride content of the ore and 31.5 per cent of the original calcite content. The final concentrate analyzed 1.2 per cent CaCO 0.15 per cent SiO and 98.07 per cent CaF The latter was 70.6 per cent of the original calcium fluoride content of the ore and about 90 per cent of the calcium fluoride content of the deslimed ore.

Example 2 The ore contained 5 per cent (32100 9 per cent SiO and 80.5 per cent CaF and was deslimed as in Example 1. The ore, however, contained a certain amount of lead and zinc values and these were removed by a preliminary frothing with 0.15 pounds of phosfphocresylic acid per ton of pulp. The roth which came over the lip of the cell during this operation was eliminated from the process and the remaining pulp was frothed as in Example 1 with 0.25 pounds of oleic acid and 0.15 pounds of cresylic acid per ton. The froth from this operation was cleaned three times as in Example 1. In this example the desliming operation removed 27.9 per cent of the original weight of the ore as slimes. These slimes contained 26.4 per cent of the original calcium fluoride content of the ore and 43.3 per cent of the original cal cite content. The final concentrate contained 0.43 per cent CaCO 0.03 per cent SiO and 99.27 per cent CaF 74.5 per cent of the original content of the ore, or practically 100 per cent of the calcium fluoride content of the deslimed ore, was recovered in the concentrate.

Example 3 sliming, 10.7 per cent of the original weight' of the ore was removed as slimes. This slime contained 8.7 per cent of the original calcium fluoride content of. the ore and 31.6 per cent of the original calcite content. The final concentrate analyzed 0.28 per cent CaCO8, 0.17 per cent SiO and 99.5 per cent CIIFz. The concentrate contained 83.3 per cent of the original calcium fluoride content of the ore and about 90 per cent of the calcite content of the deslimed ore.

It is to be understood that the above examples are given merely by way of illustration and that in its broader aspects the invention is not limited to the specific details described, but is defined by the appended claims.

We claim 1. In a process of froth-flotation for the concentration of fluorspar values from fluorspar ore containing substantial amounts of calcite, the steps comprising removing the major portion of the slimes, and frothing a v pulp, containing the deslimed ore, with oleic acid'and, a modifying agent adapted to decrease the calcite-lifting properties of the froth. e

2. In a process of froth-flotation for the concentration of fluorspar values from ores containing substantial amounts of calcite, the steps comprising grinding the ore, removing a greater part of the slimes from the said ore, and frothing a pulp, containing the ground and deslimed ore, with oleic acid and a suitable froth-tendering agent.

3. In a process of froth-flotation for the concentration of fluorspar values fromfluorspar ores containing substantial amountsof calcite, the steps comprising grinding the ore, removing a. greater part of the slimes from the said ore, and frothing a pulp, containing the ground and deslimed ore, with oleic acid and cresylic acid.

4. In aprocess of froth-flotation for the concentration of fluorspar values from fluor the ore, and frothing a pulp, containing the ground and deslimed ore, with oleic and cresylic acids in substantially equal proportlons.

6. In a froth-flotation process for concentrating the fluorspar values of ground and de-,

slimed fluorspar ores containing substa'ntiak amounts of calcite, the step comprising frothing a pulp, containing the ground and de slimed ore, with oleic acid and an agent capable of decreasing the calcite-lifting properties of the froth.

7. In a froth-flotation process forconcentrating the fluorspar values of ground and deslimed fluorspar ores containing substantial amounts of calcite, the step comprising frothing a pulp, containing the ground and deslimed ore, with oleic acid and cresylic acid.

8. In, a froth-flotation process for concentrating the fluorspar values of ground and deslimed fiuors ar ores containing substantial amounts 0 calcite, the step comprisin -frothing'a pulp, containing the ground an deslimed ore, witholeic acid and cresylic acid in substantially equal parts.

9. In a' process of froth-flotation for the concentration of fluorspar values from fiuorspar ores containing substantial amounts of calcite, the steps comprising grinding theore, forming a pulp containing the ground ore, and frothing'the pulp with oleic acid and a froth-tendering reagent adapted to decrease the calcite-lifting properties of the froth.

10. In a process of froth-flotation for the concentration of fluorspar values from fluorspar ores containing substantial amounts of calcite, the steps comprising grinding the ore, forming a pulp containlng the ground ore, and frothing the pulp with oleic and cresylic acids. 11. In a froth-flotation process for concentrating the fluorspar values of fluorspar ores containing substantial amounts of calcite, the steps comprising grinding the ore, forming pulp containing the ground ore, and frothing the pulp with oleic acid and cresylic acid in substantially equal parts.

12. 'In concentrating the fluorspar values of fluorspar or'e containing substantial amounts of calcite, finely dividing the ore,

and removing from the finely divided ore enough of the slimes to permit recovery of the fluorspar values byfrothing.

13. .In a process of froth-flotation for the concentration of fluorspar values from fluorspar ores containing substantial amounts of calcite, the improvement which consists in frothing a pulp, containing the ground ore,

with a frothing agent and a froth-tendering agent adapted to decrease the calcite-lifting properties of the froth.

In testimony whereof we hereto aflix our signatures; 7

JOHN CHARLES WILLIAMS. OMER WATSON GREEMAN. 

